The invention relates to a recording device for recording on a radiation-sensitive record carrier; and it relates, more particular, to recording an information pattern including recording areas having first optical properties which alternate with intermediate areas having second optical properties. The recording device comprises an optical write head including a scanner for scanning the record carrier with the air of a write beam; a modulator for switching the intensity of the write beam, in conformity with a bivalent signal of a specific duty cycle, between a low write intensity, which does not bring about a change in optical properties of the record carrier at the scanning location, and a high write intensity, which brings about an optically detectable change of the record carrier at the scanning location; an optical read head, including a scanner for scanning the information pattern, thus formed, with the aid of a read beam, the read beam being modulated by the information pattern being scanned, a radiation sensitive detector for converting the modulated read beam into a corresponding read signal; an analysis circuit for deriving from the read signal an analysis signal which indicates the deviation of the average ratio between the length of the recording areas and the intermediate areas relative to an optimum ratio defined by the duty cycle; and a circuit for setting the write intensity, depending on the analysis signal, to a value for which the ratio between the lengths of the recording areas and the intermediate areas substantially corresponds to the optimum ratio defined by the duty cycle.
The invention further relates to an analysis circuit for use in such a recording device. A recording device the type as described in the preceding paragraph is known, inter alia from U.S. Pat. No. 4,225,873. The prior art recording device is employed for recording signals whose average duty cycle is 50%. The magnitude of the 2nd-harmonic signal component of such signals indicates the extent to which the average ratio between the lengths of the recording areas and intermediate areas deviates from the optimum ratio defined by the duty cycle, which in that case is unity. Depending upon the magnitude of the detected 2nd-harmonic signal component, the write-intensity for a prior art recording device is set to a value for which this component is substantially zero. A drawback for such a write intensity control is that it cannot be employed for recording processes in which the width of the recording areas recorded within a recording zone is not constant but varies, as is often the case, for example, in thermal recording processes, where the width of the recording zone is larger at the end of the recording than at the beginning. When an information pattern comprising recording areas of varying width is read, this width variation gives rise to a comparatively large additional 2nd-harmonic component. As a result of this additional component, the magnitude of the 2nd-harmonic signal component can no longer be used for write-intensity control.